Manufacture of multi-layered electrical assemblies

ABSTRACT

A method for fabricating electrical component assemblies includes the steps: 
     (a) providing a first electrode and a first electrical component and locating the electrode in a recess formed by the component to produce a first laminate sub-assembly, 
     (b) providing a second electrode and a second electrical component and locating the electrode in a recess formed by the second component to produce a second laminate sub-assembly, and 
     (c) locating said two sub-assemblies in mutually stacked relation, thereby to form a resultant assembly. 
     The components are typically provided by deposition on the electrodes and to protrude edgewise thereof beyond selected edges of the electrodes, thereby to form electrical contacts, and said locating of the sub-assemblies is carried out to cause said contacts to protrude in at least two different directions from the resultant assembly. The components typically consist of dielectric material, and the electrodes are typically deposited in the form of electrically conductive ink.

BACKGROUND OF THE INVENTION

This invention relates generally to the production of multilayeredcomponents, and more particularly concerns process and apparatus toproduce multilayered electrical components; additionally, the productsproduced by the process are part of the invention.

Conventional processes for producing commercial multilayer capacitorsemploy the following steps:

1. Casting a ceramic slip by use of a doctor blade to form a green,dried ceramic film of 0.001" to 0.002" thickness;

2. Printing a registered matrix of metal pigmented inks to form theelectrodes of the finished capacitor on the ceramic film;

3. Stacking a number of the registered electrode matrices in a cavityand laminating the stack of printed ceramic sheets with pressure andheat to form a compacted structure;

4. Cutting the compacted structure as by use of a guillotine typecutter.

The number of parts generated is determined by the number of electrodesin the printing matrix;

5. Thermal processing consists of a drying and bake out cycle toeliminate the organic components from the green parts, followed by afiring cycle to 2,000° F. to 2,300° F. to form the final ceramicstructure.

6. Metallizing the ends of each individual capacitor element isnecessary to achieve the desired electronic configuration. This isaccomplished by applying a small amount of a fritted silver paint toeach end of the ceramic capacitor element. After both ends are dried,the parts are fired to form metallic surfaces by which the appropriateindividual electrodes within the ceramic are interconnected, and also bywhich the finished part may be connected to an electronic circuit.

7. Testing for the various electrical parameters completes themanufacturing process.

The controls necessary to achieve a satisfactory yield of capacitors ofa specified value are indicated by the mathematical relationshipsrelated in the design equation:

    C=0.224(nkA/d)pf                                           (1)

where,

C=capacitance of the device

n=number of active layers

k=dielectric constant of ceramic film

A=active area of an electrode (fired)

d=fired thickness of the dielectric film (in thousandth of an inch)

To achieve a given value for capacitance C one must accurately controlvalues of these parameters, as follows:

(d) Dielectric thickness (typically 0.0013"±0.0001"), and

(k) Dielectric constant. Control of this parameter is not only relatedto "lots" (i.e. differently fired groups) but also requires a verycarefully controlled firing profile for consistant results. "Lot" kvalues are statistically determined before releasing material toproduction. A number of ceramic formulations are used, each with its ownunique configuration of electrical parameters. They usually are referredto as "bodies" i.e. k1200 body would be a ceramic whose k is 1200.

(A) The active area of the electrode. In this regard, the electrodeconfiguration is usually a function of mechanical constraints since itsets the size of the capacitor. Controls relating to the electrodeconsist of using the lowest cost precious metal electrode alloyconsistent with the processing temperature and body chemistry, andcontrolling the electrode thickness. In this regard, changes inthickness cause a second order effect on capacitance. Also, if theelectrode material is too thin as applied, areas of the electrode may benon-conductive and the effective area A will be lowered.

(n) Number of active layers is important, in that once the size of thecapacitor (length and width) has been set by space available, and thedielectric type and thickness are chosen as a function of the electricalcircuit requirements, the number of layers (n) can be adjusted toachieve the design capacitance. Clearly, there are limits to the leastand most capacitance available. The upper limit of "n" for a given parttype is somewhere around 40 layers, since yield of good parts startsdeclining rapidly beyond that. Many parts with more layers are soldhowever, since high capacitance coupled with small size of a part is apremium condition and commands higher prices. It is difficult tomaintain uniform, undistorted internal structures in these high layerparts because of the green ceramic density variations introduced in themanufacturing process. These result in shrinkage variations upon firing,which produce material distortions appearing as delaminations of thelayered structure of the capacitor. This is the most serious mechanicaldefect which results from conventional production of multilayercapacitors, and one for which there is no non-destructive testavailable. If a production lot is sampled by making petrographic tests,and it is found that delaminations are occuring above a certainpercentage (it varies as a function of end use), the whole lot must bescrapped.

SUMMARY OF THE INVENTION

It is a major object of the invention to provide a new process whichgreatly simplifies the manufacture of multilayered components, as forexample by elimination of steps 4 and 6 above (these being the mostcostly from the standpoint of labor involved).

Basically, the process includes the following steps:

(a) providing a first electrode and a first electrical component andlocating the electrode in a recess formed by the component to produce afirst laminate sub-assembly,

(b) providing a second electrode and a second electrical component andlocating the electrode in a recess formed by the second component toproduce a second laminate sub-assembly, and

(c) locating said two sub-assemblies in mutually stacked relation,thereby to form a resultant assembly.

As will appear, multiple first electrodes and first components may beformed on a first decal to produce first laminate sub-assemblies;multiple second electrodes and second components may be formed on asecond decal to produce second laminate sub-assemblies; and the decalsmay be manipulated to remove first or type A sub-assemblies onto asetter, to remove the second or type B sub-assemblies to stack preciselyon the A sub-assemblies, and this may be repeated to build-up stacks ofdesired numbers of electrodes, thereby to form assemblies in the form ofcapacitors, coils, resistances, or combinations thereof.

Additional objects include the provision of methods to interconnectelectrodes in stacked sub-assemblies; to locate sub-assemblies inprecise registered relation; to build-up stacks with covering componentsat upper and lower ends of the stacks; and to achieve fabrication ofsuch assemblies of many different sizes at very low cost and at highproduction rates.

Further objects include the provision of apparatus or tooling to enablesuch fabrication, and the provision of the resultant sub-assemblies andassemblies, themselves.

These and other objects and advantages of the invention, as well as thedetails of illustrative embodiments, will be more fully understood fromthe following description and drawings, in which:

DRAWING DESCRIPTION

FIG. 1 is a flow diagram;

FIG. 2 is a plan view of a prepared decal;

FIG. 3 is plan view of the FIG. 2 decal with screen printed electrodesthereon;

FIG. 4 is a plan view of the FIG. 3 composite with "A type" electricalcomponents screen printed on the electrodes and decal;

FIG. 5 is a plan view like FIG. 4 but with "B type" components screenprinted on electrodes and on the decal;

FIG. 6 is a plan view like FIG. 4 but with "C type" components printeddirectly on the decal, i.e. with no electrodes;

FIG. 7 is an enlarged plan view of an "A type" component and electrodecomposite;

FIG. 8 is a side view of the FIG. 7 composite;

FIG. 9 is an enlarged plan view of a "B type" component and electrodecomposite;

FIG. 10 is a side view of the FIG. 9 composite;

FIG. 11 is an end view of the FIG. 9 composite;

FIG. 12 is an enlarged plan view of a "C type" component;

FIG. 13 is a side view of the FIG. 12 component;

FIG. 14 is a schematic elevational view of a screening process todeposite electrodes on a decal;

FIG. 15 is a schematic elevational view of a screening process todeposite electrical components, on the electrodes previously depositedas in FIG. 14;

FIG. 16 is a schematic elevational view of the FIG. 15 composites afterinversion on to a support, and showing peeling of the decal;

FIG. 17 is a view like FIG. 16 but showing both A and B type composites,one stacked on the other, and a decal for the upper composites beingpeeled away;

FIG. 18 is a side elevational view showing a completed multi-layeredelectrical assembly prior to firing;

FIG. 18a is like FIG. 18, but shows a completed capacitor;

FIG. 19 is a view like FIG. 7 showing a varied, i.e. A' composite;

FIG. 20 is an end view of the A' composite of FIG. 19;

FIG. 21 is a view like FIG. 9 showing a varied, i.e. B' type composite;

FIG. 22 is an end view of the FIG. 21 composite;

FIG. 23 is a view like FIG. 21, showing a varied, i.e. C₁ typecomposite;

FIG. 24 is an end view of the C₁ composite;

FIG. 25 is a view like FIG. 23 showing a further varied, i.e. C₂ typecomposite;

FIG. 26 is a view like FIG. 12 showing a blank component;

FIG. 27 is an enlarged side elevation of a stack of composites as seenin FIGS. 19-26;

FIG. 28 is a perspective view of a spiral (left handed) electrodepattern;

FIG. 29 is an elevational view of a composite which incorporates theFIG. 28 electrode;

FIG. 30 is a perspective view of a spiral (right handed) electrodepattern;

FIG. 31 is an elevational view of a composite which incorporates theFIG. 30 electrode;

FIG. 32 is an elevational view of an assembly which incorporates theFIGS. 29 and 31 composites, in alternating relation, to form a coil; and

FIG. 33 is an elevation showing a combination of assemblies.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, the process contemplates the provisionof carriers such as flexible decals 10, which are initially prepared.Such preparation, indicated at 13, may advantageously include punchingholes 11 through the rectangular decal sheets, as for example proximateto opposite corners 10a and 10b. Such holes closely fit guide posts, asare better seen at 12 in FIGS. 14-17, in order to guide the decals intoaccurate registration upon assembly of electrode and electricalcomponent composites. Typical transfer decals are formed by 6 inch by 6inch square sheets of MYLAR plastic material. The surface of the decalis further prepared by application of a thin coating of a transferrelease agent 14 as for example wax. Such agent is somewhat tacky atroom temperature to retain the composites for transfer, and may easilyrelease them in response to heating of the wax.

Next, multiple first electrodes are provided in spaced apart andsupported relation on a first carrier, i.e. a first decal 10a. This stepis indicated at 16 in FIG. 1, and FIG. 3 shows rows and columns of suchelectrodes 17 on the decal. Referring to FIG. 14, this step may becarried out by screening a fluid mix which includes the electrodematerial onto the decal. Note the screen 18, suitably supported at 19,and a template 20 on the screen with openings 21 directly over thelocations at which the mix is deposited onto decal as electrodes 17. Asqueegee blade 23 may be passed over the template, as shown, to forcefluid mix 22, through the openings 21 onto the screen and onto thedecal. Note guide posts 12 passed through registration holes in thedecal, screen and template. The electrodes may have rectangular shape,as shown, or any other desired shape. Electrode liquid mixes are knownas "inks", and representative inks are identified as Conductive Inksproduced by Du Pont, Selrex, Cladan Inc., and others. Curing of theelectrodes to said form may be accelerated under mild heating asindicated at 26 in FIG. 1. In addition, to the use of air drying inksfor both the electrode and dielectric functions, the use ofElectro-Therm inks is included. This technique enables use of an "ink"or transfer mechanism which is a solid at room temperature but is of anink-like consistancy at room temperatures 10° to 100° F. above ambient.Upon being "screened" or printed onto the substrate using a heatedscreen or template, the ink freezes to a "dry" or solid state and may beimmediately processed to the next operational step. Such a material is aproduct of the Ferro Corp., and is marketed under the name"Electro-Therm Inks".

Next, and as shown at 27 in FIG. 1, multiple electrical components A aredeposited on the formed electrodes 17 on certain decals to produce firstlaminate sub-assemblies, this step also appearing in FIG. 4. Likewise,components B are deposited on formed electrodes on other decals asindicated at 28 in FIG. 1 and in FIG. 5, to produce second laminatesub-assemblies. Typically, and extending the description to FIG. 15, thesource of the components consists of a comminuted dielectric materialsuch as a ceramic, in a liquid carrier, supplied at 29. A squeegee blade131 is passed over a template 32 to urge the liquid mix through templateopenings 33 and through a screen 34 for deposition on the electrodes. Itwill be noted that the deposition of the mix is onto part, but not all,of each electrode, and also onto the decal; for example, the electrodemay protrude at one end of the deposited material A, for example, andthe material A deposited on the decal at the opposite end of theelectrode. This is also clear from FIGS. 7 and 8 wherein an electrodelamination 17 is shown locally protruding at 17a endwise from thecomponent A lamination, the latter forming a three-sided recess 30 inwhich the remainder of the electrode is received. The component A alsoextends at the end of the electrode, i.e. at 31, for purposes as willappear. Similarly, in FIGS. 9-11, the component B forms a recess 30 inwhich another electrode 17 is received, and from which the electrodeprotrudes at 17b. FIGS. 12 and 13 illustrate a blank component C of asize corresponding to the like sizes of components A and B, so that theymay be stacked as in FIGS. 1 and 18. Step 35 in FIG. 1 indicates thescreen formation of C component, also seen in FIG. 6, A, B and Ccomponents, in the FIGS. 4-6 showings, have corresponding row and columnorientation, in the same spacial relation to decal corner openings 11,for later precision registration of the decals and components.

The components A, B and C are allowed to cure, i.e. solidify, on thedecals, as for example at room temperature, or more quickly under slightheat application (as for example by infra-red lamp heating). During suchcuring, the solvent or liquid carrier evaporates, allowing the componentparticles and resin binder to coagulate. Examples of such componentmixes are those known in the trade as dielectric pastes, and areproducts of such companies as E. I. DuPont, and Selrex.

Finally, the sub-assemblies as represented in FIGS. 4 and 5, and alsoFIG. 6, are brought into mutually stacked relation, thereby to formresultant assemblies. To this end, the carriers or decals are displacedto effect precision registration of the sub-assemblies, and the carriersare suitably removed, as by heat application and peeling away from thesub-assemblies. FIG. 16 shows sub-assemblies that embody componentmaterial B inverted and placed onto a plate 40, with predeterminedprecision location as effected by placement of decal corner openings 11onto guide posts 12a. Slight heat application, as by lamp 41, melts thetacky wax on the decal, which held the sub-assemblies thereto duringmanipulation of the decal, and allowing peel-away of the decal. Ifnecessary, a wax coating on the surface of plate 40 may be used to holdthe sub-assemblies in position. Thereafter, FIG. 17 shows precisionstacking of sub-assemblies embodying components A onto thesub-assemblies embodying components B, by inversion and placement ofdecal 10b into the position shown, with corner holes on posts 12a.Peel-away of the decal is also shown.

In this manner, a built-up stack or assembly as shown at 44 in FIG. 18may quickly be realized. Note that the stack is formed with tabs ofsuccessive electrodes in the stack exposed at opposite ends of thestack. No large laminating force, i.e. to compress the stack, isrequired because the metal electrode in each sub-assembly is flush withits associated component or dielectric surface, as explained above. Thisthen obviates or prevents density distortions which in the past have ledto serious delamination problems. FIGS. 17 and 18 also show the stackson a setter 40 upon which drying and firing of the stacks takes place.This eliminates hand loading which was previously required to maintainthe parts in separated relation so as not to fuse together.

The exposed electrode tabs at each end of the stack melt and fusetogether during the bake-out cycle, whereby alternate electrodes areelectrically joined, at 17a' and 17b' to form a capacitor, as seen inFIG. 18a. Many different and more complex configurations can be made inthis manner, and in both large, medium and small sizes.

The preceding drawing descriptions have concerned quite simpleelectrodes for conceptual purposes. In actual practice, a morecomplicated electrode configuration can be used, as shown in FIGS.19-27. In FIGS. 19 and 20 the flat electrode 51 has T shape or outline,the "stem" 51a of the T located inwardly of the outer sides 52a and end52b of ceramic lamination or component 52. Note that the electrode is"sunk" in a recess 52d formed by the component 52 so that the underside51c of the electrode is flush with the underside 52c of the component52. The cross-bar 51d of the T-shaped electrode protrudes at theopposite end of the component 52, and also protrudes laterally beyondthe laterally opposite sides 52a. This sub-assembly is designated "A". Asimilar "B" sub-assembly is shown in FIGS. 21 and 22, the differencebeing that the A and B electrode cross-bars are located at opposite endsof the ceramic components. The C₁ sub-assembly of FIGS. 23 and 24differs in that the electrode material 53 overlaps and stands out abovethe end surface of the ceramic component 54. Also, it protrudes endwiseat 53a, as seen in FIG. 27. This C₁ sub-assembly is adapted to form anupper "cover" in the stack formed as shown in FIG. 27. The FIG. 25 C₂sub-assembly again differs in that the electrode material 55 is "sunk"in a recess 57 formed by ceramic component 56, as seen in FIG. 27; alsothe electrode material protrudes endwise at 55a. C₂ forms a lower coverat the stack. FIG. 26 shows a blank ceramic component 58, and is alsoshown in the stack between cover C₂ and a sub-assembly A.

Upon heating of the formed stack, as during firing, the protrudingelectrodes 53a, 51d and 55a soften and fuse together, as indicated bydotted line 59. The same thing occurs at the opposite ends of thesub-assemblies at the opposite side of the FIG. 27 stack. A multi-platecapacitor is thereby formed. Note that electrode material associatedwith the covers C₁ and C₂ is exposed at opposite ends of the stack.

The result of using this FIG. 27 electroding configuration is theformation of the end terminations at the same time as the stack isfired. This has more significance than merely the elimination of onestep. For example, the sizes of capacitors at the small end of thespectrum is limited by the difficulty of silvering the tiny pieces. Thisnew approach allows a five-fold reduction in size, i.e. the lower sizelimit would be approximately 0.010" square. Also part shapes would notbe limited to parallelapipeds or cylinders; i.e. literally any areashape is possible.

This new process also permits all the in-process step controls that theconventional system does. It allows the inspection of both the electrodeprint and dielectric print for perfection and thickness beforecommitment to actual construction (something the spray type systems donot do). It also makes possible the use of thinner dielectric because ofthe electrode/dielectric configuration (embedded electrode). This makespossible the provision of a 25 volt capacitor designed to take advantageof the lower voltage (four times the capacitance for a given volume, orless than half the precious electrode material required, for the samecapacitance) rather than just elevating a 50 volt unit.

The elimination of the cutting operation also enables the production ofa more "reliable" part for high reliability requirements. One of themajor concerns of recent high reliability studies performed by HughesAircraft Co., for the U.S. Navy is the presence of small micro cracksthat can be detected on the cover plate surfaces adjacent to thesilvered ends of the capacitors. They occur randomly on parts in a givenlot, and are not detectible except by visual inspection magnified 400times or more. Such cracks have proven to be the loci of a number offailure modes experienced in life testing. The source of these cracks isthe cutting operation, which is eliminated by the present invention.

Besides reducing the number of steps required to manufacturer partsalong with the lower capital investment required, a list of advantagesfor the new system is as follows:

1. Smaller parts possible to fabricate.

2. Lower voltage ratings.

3. No shape limitations.

4. In process inspection enhanced.

5. Elimination of cutting stress cracks.

6. Elimination of internal delamination caused by laminating stressdisturbing green density.

7. Lower labor "content" per part, i.e. less labor required tofabricate.

8. End terminations of electrodes enable provision of a variety of tabconfigurations with no extra process time.

9. Inventory can partially be carried in decal form, allowing for rapidresponse to customers. Thus, the decals can be processed as in FIGS. 16and 17 to build-up capacitor plates and configurations, as required.

10. The invention enables provision of a line of capacitors adapted touse with semi-conductor devices, mounted on the silicon substrates suchas LSI devices in watches, calculators multi processors, etc.

The procedure described above, used to manufacturer multilayer ceramiccapacitors, is also adaptable to a number of other electronic ceramicdevices. An example would be multilayer ferrite inductors.

Referring to FIGS. 28-32, the method of producing an electrical coilincludes the following basic steps:

(a) forming multiple laminates, each laminate including electricallyconductive material in the form of a portion of a coil, andnon-conducting material laminated to said electrically conductivematerial, and

(b) stacking said laminates so that said coil portions are located forelectrical interconnection to form coil structure.

In FIG. 28 a left handed spiral coil "electrode" pattern 70 is initiallyformed on a decal 71 in the manner described above; similarly a righthanded spiral coil pattern 72 is formed on a decal 73, as seen in FIG.30. FIGS. 29 and 31 show deposition of ferrite ceramic "component"material 74 and 75 on the two coils, to form composites "A" and "B". Theformation of stack 75 shown in FIG. 32 involves stacking the upright Aand inverted B composites. The coils have end terminations 76 and 77which protrude at edges of the composites as shown in FIGS. 29, 31 and32. Similarly, the coils have terminations 76' and 77' which are spacedinwardly from the edges of the composites. Terminations 77' extend allthe way through the components 75 so as to contact terminations 76'.After heating, the interengaged terminations become fused to provide acomplete coil. Laborious and expensive winding of coils is therebyobviated, and many sizes of coils can be easily fabricated at low cost.

Interleaving patterns would produce transformer configurations, magneticamplifiers, saturable reactors, solenoids, memory cores, etc.

Another example would be multilayer substrates which are layered ceramicstructures with buried metal circuitry.

Another possibility is semiconductor packages, such as the dual lineconfigured packages.

A further possibility is the fabrication of precision resistors, i.e.with electrically resistive material constituting the "electrodes". Forexample, series connected resistors may be provided as in the FIG. 32stack, or in another arrangement of electrodes. Series connectedresistors and coils may be provided in this way, too, and capacitors maybe included, all in one stack. See FIG. 33 in this regard.

I claim:
 1. An electrical assembly comprising(a) a first stack oflaminar components, (b) a second stack of laminar components, (c) saidstack including laminar elements forming electrical elements consistingof stabilized ink, the electrical elements of the two stacks beingconnected at one end at least of each stack, (d) each electrical elementselected from the group that includes resistance, capacitance andinductance, (e) said laminar components including dielectric components,the electrical elements embedded in associated dielectric componentsexcepting for end portions of the electrical elements that protrudebeyond the ends of the dielectric components, each dielectric componentformed as a unitary layer so that the electrical element has only oneexposed side surface located in a plane formed by its associateddielectric component material adjacent two spaced apart edges of theelectrical element and adjacent one end of the electrical element remotefrom said end portion, (f) the said protruding end portions of thestabilizer ink electrical elements being connected as defined, saidconnected end portions characterized as fused together adjacent saidends of the stacks.